Technical Field
The present disclosure relates to a digital electronic interface circuit for an acoustic transducer and to a corresponding acoustic transducer system.
Description of the Related Art
Acoustic transducers, for example MEMS (microelectromechanical system) microphones, are known, including a micromechanical sensing structure, designed to transduce acoustic pressure waves into an electrical quantity (for example, a capacitive variation), and a reading electronics, designed to carry out suitable processing operations (amongst which amplification and filtering operations) of the electrical quantity so as to supply an electrical output signal, either analog (for example, a voltage) or digital (for example, a PDM—pulse density modulation—signal).
This electrical signal, possibly further processed by an electronic interface circuit, is then made available for an external electronic system, for example a microprocessor control circuit of an electronic apparatus incorporating the acoustic transducer.
The micromechanical sensing structure in general includes a mobile electrode, provided as a diaphragm or membrane, set facing a fixed electrode to provide the plates of a variable-capacitance detection capacitor. The mobile electrode is generally anchored, by means of a perimetral portion thereof, to a substrate, whilst a central portion thereof is free to move or deflect in response to the pressure exerted by incident acoustic pressure waves. The mobile electrode and the fixed electrode provide a capacitor, and the deflection of the membrane that constitutes the mobile electrode causes a variation of capacitance as a function of the acoustic signal to be detected.
In general, the electrical performance of the acoustic transducer depends on the mechanical characteristics of the sensing detection structure, and moreover on the configuration of the associated, front and rear, acoustic chambers, i.e., of the chambers facing a respective, front or rear, face of the membrane, and traversed in use by the pressure waves that impinge upon the membrane and that move away therefrom.
There are numerous applications in which detection of acoustic-pressure waves with a wide dynamic range are used, i.e., the possibility of detecting signals with a high sound-pressure level (SPL), while maintaining high values of the signal-to-noise ratio (SNR), and signals with a low sound-pressure level with a high sensitivity.
Basically, a frequently important design rule is to optimize the compromise between obtaining a wide dynamic range in detection of the acoustic-pressure waves and obtaining a low signal-to-noise ratio.
U.S. Pat. No. 6,271,780 discloses, in this connection, a solution for increasing the dynamic range in an acoustic system, comprising an analog-to-digital converter (ADC), designed to receive an analog detection signal from an acoustic transducer. This solution envisages subjecting the analog input signal, in parallel, to two signal-processing paths, which have a first, analog, portion and a second, digital, portion, and each of which has a respective amplification and gain factor so as to adapt, respectively, to signals with a low, or a high, acoustic pressure level. The two digital signals at output from the two processing paths are recombined to supply a resulting output signal. Prior to the operation of recombination, the two signals undergo an operation of equalization to take into account differences of gain, offset, and phase generated by the previous operations of signal processing, in part of an analog type, and thus prevent distortion of the resulting output signal.
This solution is not free from problems, due mainly to the complexity of the processing chain, to a relevant sensitivity to noise and oscillations of the input signal, and to a reduced configurability.
In general, it is thus certainly felt to provide an improved solution for extending the dynamic range in the detection of acoustic-pressure waves via an acoustic transducer.